Mining and construction machines such as backhoe loaders and excavators employ various implements, such as buckets, rams, forks, grapples, thumbs, etc., to perform different operations. For example, a machine may use counteracting thumbs and buckets to grasp, hold, and lift odd-shaped articles such as pipes, structural components, and the like. Hydraulic actuators typically control these thumbs and buckets. Due to different kinematics and varying cylinder geometry, moving the bucket and thumb together in a coordinated manner is not easy. For example, if the hydraulic actuators for the thumb and the bucket are both extended the same amount, the thumb may move a different angular distance than the bucket. Moreover, the hydraulic actuators for the thumb and the bucket may extend or retract at different rates given the same flow of hydraulic fluid.
Methods have been proposed to attempt to coordinate the linkage motion between the thumb and the bucket. For example, U.S. Pat. No. 6,385,870 to Webel (“Webel”) discloses a control system for an excavator thumb and a method of controlling an excavator thumb. Webel uses a thumb control circuit that is activated by the press of a button and maintains a constant reduced close fluid pressure of the extend port of the thumb cylinder until the open control is actuated.
While Webel provides a technique that seeks to maintain a constant thumb cylinder pressure as the bucket rotates, Webel requires activation of a separate switch. In addition, the hydraulic circuit of Webel requires complex circuitry and plumbing that may not be suitable for retrofit applications.
The present invention is directed to overcome one or more of the problems as set forth above.